Tropical Depression SIXTEEN (Text)

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TROPICAL DEPRESSION SIXTEEN DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL162010
500 AM EDT WED SEP 29 2010
ALTHOUGH THE SATELLITE APPEARANCE OF TROPICAL DEPRESSION SIXTEEN HAS
CHANGED LITTLE SINCE THE LAST ADVISORY...DOPPLER RADAR DATA FROM
KEY WEST AND MIAMI...ALONG WITH RADAR RADAR FROM CUBA INDICATE
CONVECTION HAS INCREASED IN THE NORTHERN SEMICIRCLE. ALSO...AN AIR
FORCE RESERVE RECONNAISSANCE AIRCRAFT FLYING BETWEEN FLORIDA AND
CUBA HAS INDICATED SURFACE WINDS OF 33 KT IN UNCONTAMINATED SFMR
DATA ABOUT 80-120 NMI EAST-NORTHEAST OF THE CENTER...WHICH IS MUCH
CLOSER TO THE CENTER THAN SEEN NOTED IN PRIOR SURFACE OBSERVATIONS
AND RECON DATA. THE LARGEST DOPPLER RADAR VELOCITY VALUES DETECTED
THUS FAR HAVE BEEN 40-44 KT BETWEEN 6000-12000 FT. THIS INDICATES
THAT THE DEPRESSION IS VERY NEAR BECOMING A TROPICAL STORM.
THE DEPRESSION IS ON TRACK AND THE THE INITIAL MOTION ESTIMATE IS
020/12. 00Z UPPER-AIR DATA AND WATER VAPOR IMAGERY INDICATED THE
MID- TO UPPER-LEVEL FLOW ACROSS THE EASTERN GULF OF MEXICO...THE
SOUTHEASTERN U.S. AND THE EXTREME NORTHWESTERN CARIBBEAN SEA HAS
BEEN STEADILY BACKING AROUND FROM THE WEST TO THE SOUTH-SOUTHWEST
DURING THE PAST 24 HOURS. AS A SERIES OF STRONG SHORTWAVE TROUGHS
DIG SOUTHWARD DOWN THE WEST SIDE OF THE LONGWAVE TROUGH LOCATED
ALONG 85W...THE FLOW ACROSS FLORIDA SHOULD BECOME MORE SOUTHERLY.
THIS FLOW PATTERN SHOULD ACCELERATE THE DEPRESSION TO THE
NORTH-NORTHEAST ACROSS SOUTHEASTERN FLORIDA AS A TROPICAL CYCLONE
TODAY...AND INTO THE CAROLINAS AS AN EXTRATROPICAL LOW PRESSURE
SYSTEM IN 36 HOURS OR SO. ALTHOUGH THE MODEL CONSENSUS HAS SHIFTED
A LITTLE TO THE EAST IN THE LATEST MODEL RUNS...THE STRONG BACKING
FLOW PATTERN MENTIONED PREVIOUSLY ARGUES FOR KEEPING THE FORECAST
TRACK ALONG THE WESTERN OR LEFT SIDE OF THE MODEL GUIDANCE
ENVELOPE. AS A RESULT...THE OFFICIAL FORECAST TRACK IS JUST AN
EXTENSION OF THE PREVIOUS ADVISORY TRACK.
THE VERTICAL SHEAR IS EXPECTED TO DECREASE SLIGHTLY DURING THE NEXT
12 HOURS BEFORE INCREASING TO ABOVE 30 KT IN ABOUT 36 HOURS. AS A
RESULT...THERE WILL BE A BRIEF WINDOW OF OPPORTUNITY FOR SOME
STRENGTHENING TO OCCUR PRIOR TO THE CYCLONE MAKING LANDFALL ALONG
THE SOUTHEASTERN FLORIDA COAST LATER TODAY. EXTRATROPICAL
TRANSITION IS EXPECTED TO BEGIN IN 24 HOURS OR SO AND BE COMPLETE
BY 36-48 HR AS THE SYSTEM NEARS THE COAST OF THE CAROLINAS WHERE IT
IS EXPECTED TO MERGE WITH A FRONTAL SYSTEM. BY 48 HOURS...THE LOW
IS FORECAST TO BE ABSORBED BY A LARGER U. S. BAROCLINIC OVER THE
NORTHEASTERN UNITED STATES. THE OFFICIAL INTENSITY FORECAST IS
SIMILAR TO THE PREVIOUS ADVISORY AND IS A BLEND OF THE SHIPS AND
LGEM INTENSITY MODELS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 29/0900Z 23.3N 81.4W 30 KT
12HR VT 29/1800Z 25.2N 80.7W 35 KT
24HR VT 30/0600Z 28.9N 79.7W 40 KT
36HR VT 30/1800Z 33.8N 78.6W 40 KT...POST-TROP/EXTRATROP
48HR VT 01/0600Z 40.0N 77.3W 35 KT...POST-TROP/EXTRATROP
72HR VT 02/0600Z...DISSIPATED
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FORECASTER STEWART
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